A High-electron-mobility transistor (HEMT), also known as hetero-structure FET (HFET) or modulation-doped FET (MODFET) incorporates a junction between two materials with different band gaps (i.e. a heterojunction) as a channel instead of a doped region as in most of metal-oxide-semiconductor field-effect transistor (MOSFET). HEMTs are capable of operating at high frequencies up to millimeter wave frequencies, and are used in high-frequency products.